A Cluster is a group of logical objects, each of which is called a
Node in Senlin’s terminology. A cluster can contain zero or more
nodes. A cluster has a profile_id
property that specifies which
Profile to use when new nodes are created as members the cluster.
Senlin provides APIs and command line supports to manage the cluster membership. Please refer to Cluster Membership for details. Senlin also supports attaching Policy objects to a cluster, customizing the policy properties when attaching a policy to a cluster. Please refer to Cluster-Policy Bindings for details.
The following command shows the clusters managed by the Senlin service:
$ senlin cluster-list
+----------+------+--------+---------------------+
| id | name | status | created_at |
+----------+------+--------+---------------------+
| 2959122e | c1 | ACTIVE | 2015-05-05T13:27:28 |
| 092d0955 | c2 | ACTIVE | 2015-05-05T13:27:48 |
+----------+------+--------+---------------------+
Note that the first column in the output table is a short ID of a cluster
object. Senlin command line use short IDs to save real estate on screen so
that more useful information can be shown on a single line. To show the full
ID in the list, you can add the -F
(or --full-id
) option
to the command:
$ senlin cluster-list -F
+--------------------+------+--------+---------------------+------------+
| id | name | status | created_at | updated_at |
+--------------------+------+--------+---------------------+------------+
| 2959122e-11c7-.... | c1 | ACTIVE | 2015-05-05T13:27:28 | None |
| 092d0955-2645-.... | c2 | ACTIVE | 2015-05-05T13:27:48 | None |
+--------------------+------+--------+---------------------+------------+
You can specify the sorting keys and sorting direction when list clusters,
using the option --sort
(or -o
). The --sort
option accepts a string of format key1[:dir1],key2[:dir2],key3[:dir3]
,
where the keys used are cluster properties and the dirs can be one of asc
and desc
. When omitted, Senlin sorts a given key using asc
as the
default direction.
For example, the following command instructs the senlin command
line to sort clusters using the name
property in descending order:
$ senlin cluster-list -o name:desc
When sorting the list of clusters, you can use one of name
, status
,
init_at
, created_at
and updated_at
.
The senlin command line also provides options for filtering the
cluster list at the server side. The option --filters
(or
-f
) can be used for this purpose. For example, the following command
filters clusters by the status
field:
$ senlin cluster-list -f status=ACTIVE
+----------+------+--------+---------------------+
| id | name | status | created_at |
+----------+------+--------+---------------------+
| 2959122e | c1 | ACTIVE | 2015-05-05T13:27:28 |
| 092d0955 | c2 | ACTIVE | 2015-05-05T13:27:48 |
+----------+------+--------+---------------------+
The option --filters
accepts a list of key-value pairs separated by
semicolon (;
), where each key-value pair is expected to be of format
<key>=<value>
. The valid keys for filtering include: status
, name
,
project
and user
.
In case you have a huge collection of clusters, you can limit the number of
clusters returned from Senlin server each time, using the option
--limit
(or --l
). For example:
$ senlin cluster-list -l 1
+----------+------+--------+---------------------+
| id | name | status | created_at |
+----------+------+--------+---------------------+
| 2959122e | c1 | ACTIVE | 2015-05-05T13:27:28 |
+----------+------+--------+---------------------+
Another option you can specify is the ID of a cluster after which you want to
see the returned list starts. In other words, you don’t want to see those
clusters with IDs that is or come before the one you specify. You can use the
option --marker
(or -m
) for this purpose. For
example:
$ senlin cluster-list -l 1 -m 2959122e-11c7-4e82-b12f-f49dc5dac270
+----------+------+--------+---------------------+
| id | name | status | created_at |
+----------+------+--------+---------------------+
| 092d0955 | c2 | ACTIVE | 2015-05-05T13:27:48 |
+----------+------+--------+---------------------+
Only 1 cluster record is returned in this example and its UUID comes after the the one specified from the command line.
To create a cluster, you need to provide the ID or name of the profile to be associated with the cluster. For example:
$ senlin cluster-create --profile qstack c3
+------------------+--------------------------------------+
| Property | Value |
+------------------+--------------------------------------+
| created_at | None |
| data | {} |
| desired_capacity | 0 |
| domain | None |
| id | 60424eb3-6adf-4fc3-b9a1-4a035bf171ac |
| max_size | -1 |
| metadata | {} |
| min_size | 0 |
| name | c3 |
| nodes | |
| profile_id | bf38dc9f-d204-46c9-b515-79caf1e45c4d |
| profile_name | qstack |
| project | 333acb15a43242f4a609a27cb097a8f2 |
| status | INIT |
| status_reason | Initializing |
| timeout | None |
| updated_at | None |
| user | 0b82043b57014cd58add97a2ef79dac3 |
+------------------+--------------------------------------+
From the output you can see that a new cluster object created and put to
INIT
status. Senlin will verify if profile specified using the option
--profile
(or -p
) does exist. The
server allows the <PROFILE>
value to be a profile name, a profile ID or
the short ID of a profile object. If the profile is not found or multiple
profiles found matching the value, you will receive an error message.
When creating a cluster, by default senlin will create a cluster
with no nodes, i.e. the desired_capacity
will be set to 0. However, you
can specify the desired capacity of the cluster, the maximum size and/or the
minimum size of the cluster. The default value for min_size
is 0 and the
default value for max_size
is -1, meaning that there is no upper bound for
the cluster size.
The following command creates a cluster named “test_cluster
”, with its
desired capacity set to 2, its minimum size set to 1 and its maximum size set
to 3:
$ senlin cluster-create -n 1 -c 2 -m 3 -p myprofile test_cluster
Senlin API and Senlin engine will validate the settings for these capacity arguments when receiving this request. An error message will be returned if the arguments fail to pass this validation, or else the cluster creation request will be queued as an action for execution.
When desired_capacity
is not specified and min_size
is not specified,
Senlin engine will create an empty cluster. When either desired_capacity
or min_size
is specified, Senlin will start the process of creating nodes
immediately after the cluster object is created.
You can use the option --metadata
(or -M
) to associate
some key-value pairs to the cluster to be created. These data are referred to
as the “metadata” for the cluster.
Since cluster operations may take some time to finish when being executed and
Senlin interacts with the backend services to make it happen, there needs a
way to verify whether an operation has timed out. When creating a cluster
using the senlin command line tool, you can use the option
--timeout
(or -t
) to specify the
default time out in number of seconds. This value would be the global setting
for the cluster.
When there are clusters in the Senlin database, you can request Senlin to show the details about a cluster you are intested in.
You can use the name, the ID or the “short ID” of a cluster to name a cluster for show. Senlin API and engine will verify if the identifier you specified can uniquely identify a cluster. An error message will be returned if there is no cluster matching the identifier or if more than one cluster matching it.
An example is shown below:
$ senlin cluster-show c3
+------------------+--------------------------------------+
| Property | Value |
+------------------+--------------------------------------+
| created_at | 2015-07-07T03:30:53 |
| data | {} |
| desired_capacity | 0 |
| domain | None |
| id | 2b7e9294-b5cd-470f-b191-b18f7e672495 |
| max_size | -1 |
| metadata | {} |
| min_size | 0 |
| name | c3 |
| nodes | b28692a5-2536-4921-985b-1142d6045e1f |
| | 4be10a88-e340-4518-a9e1-d742c53ac37f |
| profile_id | bf38dc9f-d204-46c9-b515-79caf1e45c4d |
| profile_name | qstack |
| project | 333acb15a43242f4a609a27cb097a8f2 |
| status | ACTIVE |
| status_reason | Node stack2: Creation succeeded |
| timeout | None |
| updated_at | None |
| user | 0b82043b57014cd58add97a2ef79dac3 |
+------------------+--------------------------------------+
From the result, you can examine the list of nodes (if any) that are members of this cluster.
Once a cluster has been created, you change its properties using the senlin command line. For example, to change the name of a cluster, you can use the following command:
$ senlin cluster-update -n web_bak web_servers
You can change the timeout
property using option --timeout
(or
-t
) for the cluster-update
command. You can change the metadata
associated with cluster using option --metadata
(or -M
).
Using the cluster-update command, you can change the profile used by the cluster and its member nodes. The following example launches a global update on the cluster for switching to a different profile:
$ senlin cluster-update -p fedora21_server web_cluster
Suppose the cluster web_cluster
is now using a profile of type
os.nova.server
where a Fedora 20 image is used, the command above will
initiate a global upgrade to a new profile where a Fedora 21 image is used.
Senlin engine will verify whether the new profile has the same profile type
with that of the existing one and whether the new profile has a well-formed
spec
property. If everything is fine, the engine will start a node level
profile update process. The node level update operation is subject to policy
checkings/enforcements when there is an update policy attached to the cluster.
Please refer to Policies and Cluster-Policy Bindings for more
information.
The senlin tool supports several different commands to resize a cluster.
cluster-resize
¶The command cluster-resize takes several arguments that allow you to resize a cluster in various ways:
min_size
and/or max_size
property of a cluster when
resizing it;You can specify one and only one of the following options for the cluster-resize command:
--capacity
(-c
) to specify
the exact value of the new cluster size;--adjustment
(-a
) to
specify the relative number of nodes to add/remove;--percentage
(-p
) to
specify the percentage of cluster size change.The following command resizes the cluster test_cluster
to 2 nodes,
provided that the min_size
is less than or equal to 2 and the max_size
is either no less than 2 or equal to -1 (indicating that there is no upper
bound for the cluster size). This command makes use of the option
--capacity
(or -c
), where
<CAPACITY>
is the new size of the cluster:
$ senlin cluster-resize -c 2 test_cluster
Another way to resize a cluster is by specifying the --adjustment
(or -a
) option, where <ADJUSTMENT>
can be a positive or a negative integer giving the number of nodes to add or
remove respectively. For example, the following command adds two nodes to the
specified cluster:
$ senlin cluster-resize -a 2 test_cluster
The following command removes two nodes from the specified cluster:
$ senlin cluster-resize -a -2 test_cluster
Yet another way to resize a cluster is by specifying the size change in
percentage. You will use the option --percentage
(or
-p
for this purpose. The <PERCENTAGE>
value can be
either a positive float value or a negative float value giving the percentage
of cluster size. For example, the following command increases the cluster size
by 30%:
$ senlin cluster-resize -p 30 test_cluster
The following command decreases the cluster size by 25%:
$ senlin cluster-resize -p -25 test_cluster
Senlin engine computes the actual number of nodes to add or to remove based on
the current size of the cluster, the specified percentage value, the
constraints (i.e. the min_size
and the max_size
properties).
When computing the new capacity for the cluster, senlin engine will determine the value based on the following rules:
min_size
and max_size
,
inclusively, unless option --strict
(or -s
) is specified;min_size
and/or max_size
is given, or else Senlin
will first verify the new size constraints and perform range checking
against the new constraints;--min-step
(or -t
) is
specified, the <MIN_STEP>
value will be used if the absolute value of
the new capacity value is less than <MIN_STEP>
.If option --strict`
(or -s
) is specified, Senlin will
strictly conform to the cluster size constraints. If the capacity value falls
out of the range, the request will be rejected. When --strict
is set
to False, Senlin engine will do a resize on a best-effort basis.
Suppose we have a cluster A with min_size
set to 5 and its current size is
7. If the new capacity value is 4 and option --strict
is set to
True
, the request will be rejected with an error message. If the new
capacity value is 4 and the option --strict
is not set, Senlin will
try resize the cluster to 5 nodes.
Along with the cluster-resize command, you can specify the new size
constraints using either the option --min-size
(or -n
) or
the option --max-size
(or -m
) or both.
cluster-scale-in
and cluster-scale-out
¶The cluster-scale-in command and the cluster-scale-out
command are provided for convenience when you want to add specific number of
nodes to a cluster or remove specific number of nodes from a cluster,
respectively. These two commands both take an argument <COUNT>
which is a
positive integer giving the number of nodes to add or remove. For example, the
following command adds two nodes to the web_servers
cluster:
$ senlin cluster-scale-out -c 2 web_servers
The following command removes two nodes from the web_servers
cluster:
$ senlin cluster-scale-in -c 2 web_servers
The option --count
(-c
) is optional. If
this option is specified, Senlin will use it for cluster size change, even
when there are scaling policies attached to the cluster. If this option is
omitted, however, Senlin will treat it as implicitly set to value 1.
A cluster can be deleted using the command cluster-delete, for example:
$ senlin cluster-delete my_cluster
Note that in this command you can use the name, the ID or the “short ID” to
specify the cluster object you want to delete. If the specified criteria
cannot match any clusters, you will get a ClusterNotFound
error. If more
than one cluster matches the criteria, you will get a MultipleChoices
error.
When there are nodes in the cluster, the Senlin engine will launch a process to delete all nodes from the cluster and destroy them before deleting the cluster object itself.
There are other operations related to clusters. Please refer to the following links for operations related to cluster membership management and the creation and management of cluster-policy bindings:
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